This application is based on Japanese Patent Application No. 11-246997 filed Sep. 1, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a process of forming an annular member such as a ring used for a manufacturing desired products such as automotive vehicle parts, or used as blanks that are to be cold-forged to manufacture desired products.
2. Discussion of Related Art
There are available various processes of forming an annular member as described below. One of the known processes includes a blanking operation and a piercing operation. In this process, a strip 10 supplied from a coil of strip is subjected to a blanking operation to punch out a plurality of workpieces in the form of circular plates 12 while the strip 10 is fed, as shown in FIG. 1A. Each circular plate 12 has the same outside diameter and outer profile as a desired ring member 14 to be manufactured. In the left half of FIG. 1B (on the left side of a one-dot chain line indicated in the figure), the circular plate 12 is shown in cross section. Then, the circular plate 12 is subjected to a piercing operation to remove a radially inner portion thereof, for thereby obtaining the ring member 14, as shown in cross section in the right half of FIG. 1B. The diameter of the radially inner portion to be removed by piercing is equal to the inside diameter of the ring member 14. However, the process including the blanking and piercing operations described above suffers from a considerably low yield ratio.
Another known process of forming a ring member includes a blanking operation, a compressing operation and a piercing operation. In this process, the strip 10 is initially subjected to a blanking operation to punch out a plurality of workpieces also in the form of circular plates 18 each of which has an outside diameter smaller than that of a desired ring member 16 to be manufactured, as shown in FIGS. 2A and 2B. In the left half of FIG. 2B (on the left side of a one-dot chain line indicated in the figure), the circular plate 18 is shown in cross section. Then, the circular plate 18 is subjected to a compressing operation to compress a radially inner portion thereof, as sown in the right half of FIG. 2B, for thereby reducing the thickness of the radially inner portion and enlarging the diameter of the circular plate 18 to the outside diameter of the ring member 16. Finally, the compressed circular plate 18 is subjected to a piercing operation to remove a radially inner portion thereof, for thereby obtaining the ring member 16, as shown in cross section in the right half of FIG. 2C. The diameter of the inner portion to be removed by piercing is equal to the inside diameter of the ring member 16. This process assures a comparatively high degree of hardness of the ring member 16 owing to the compressing operation on the circular plate 18, leading to improved strength of the product to be manufactured from the ring member 16. Further, this process assures a higher yield ratio than the process of FIGS. 1A and 1B. However, the yield ratio in the process of FIGS. 2A-Ac is still unsatisfactory. Further, the present process is not applicable to a strip (blank sheet) having a comparatively small thickness.
A further alternative known process for forming a ring member includes a roll bending operation on a strip. Described more specifically referring to FIGS. 3A-3C, a plurality of narrow strips 20 shown in cross section in FIG. 3A each having a relatively small width are formed from the strip 10. Each narrow strip 20 is formed into an annular member by roll bending. The thus obtained annular member has a seam 22, as indicated in FIG. 3B. Finally, the annular member is subjected to a calking operation or a welding operation at the seam 22, to thereby form a ring member 24 as shown in FIG. 3C. This process assures a significantly improved yield ratio. In the presence of the seam 22 on the ring member 24, however, the present process suffers from a low strength of the product to be manufactured from the ring member 24. Further, the process is not applicable to a strip having a comparatively large thickness.
JP-A-2-27058 discloses a further alternative process of forming a ring member, which includes a forging operation on one longitudinal end portion of a blank in the form of a round bar, and a shearing operation on the formed longitudinal end portion. Described in detail, the longitudinal end portion of the round bar is subjected to a forging operation with a die set including a female die and a male die, such that a punch portion of the male die is moved into a die hole of the female die, to cause deformation of the longitudinal end portion of the rod held in the die hole, so that a circular recess is formed in the end face of the end portion of the rod. Thus, the circular recess is defined by the annular wall whose outside diameter is larger than the original diameter of the rod. The thus forged longitudinal end portion of the rod is subjected to a shearing operation to cut off only the annular wall portion from the forged end portion of the rod, whereby a ring member constituted by the annular wall is obtained. Where the diameter or transverse cross sectional area of the round rod is comparatively large, a large forging force is required to be applied to the longitudinal end portion, for forming the above-indicated recess defined by the annular wall. Therefore, the present process is not available when the ring member to be manufactured has a comparatively large outside diameter.
It is therefore an object of the present invention to provide a process which permits an annular member to be formed with a sufficiently high yield ratio, with reduced limitations in the diameter and thickness of the ring member.
The above object may be achieved according to the principle of the present invention, which provides a process of forming at least one annular member from a cylindrical member, comprising the steps of: (a) applying a force to said cylindrical member in an axial direction thereof, to thereby cause plastic deformation at one of opposite axial end portions of the cylindrical member, such that a flange extends in a generally radial direction from one of opposite axial ends of the cylindrical member which corresponds to the above-indicated one of the opposite axial end portions; and (b) effecting a shearing operation on the flange to punch out the annular member.
In the process of the present invention, an axial force is applied to the cylindrical member in its axial direction, in the plastic deformation step, so as to cause plastic deformation at one axial end portion thereof, such that a flange extends from the corresponding one axial end of the cylindrical member in a generally radial direction of the cylindrical member. In the next shearing step, the flange is subjected to a shearing operation to punch out the desired annular member. Therefore, the present process permits the annular member to be formed with reduced limitations in the size and thickness of the annular member.
In a first preferred form of the present invention, a plurality of annular members are successively formed from the cylindrical member, such that the step of applying a force to the cylindrical member and the step of effecting a shearing operation are repeatedly implemented after a first one of the plurality of annular members is punched out. In this instance, the cylindrical member whose flange has been subjected to the shearing operation to punch out each annular member is subjected to the plastic deformation so as to again form the radially extending flange, and this flange is again subjected to a shearing operation to punch out the next one of the plurality of annular members. The process according to the present preferred form of the invention assures a relatively high yield ratio of the annular members.
In a second preferred form of this invention, the process further comprises a step of preparing the cylindrical member which includes a cylindrical wall and an inward flange as the above-indicated flange at one of opposite axial ends of the cylindrical wall, the inward flange being formed by plastic deformation when the cylindrical member is formed such that the inward flange extends radially inwardly of the cylindrical wall, and wherein the inward flange as formed by plastic deformation is further subjected to plastic deformation in the above-indicated step of applying a force to the cylindrical member and the above-indicated step of effecting a shearing operation. In this arrangement, the inward flange is first subjected to the plastic deformation when the cylindrical member with this inward flange is formed, and is again subjected to the plastic deformation with an axial force applied to the cylindrical member such that the material of the corresponding axial end portion of the cylindrical member flows in the radially inward direction of the cylindrical wall. Accordingly, the ring member punched out from the inward flange has an increased strength.
In one advantageous arrangement of the second preferred form of the invention, the cylindrical member with the inward flange is formed by the steps of: subjecting a strip to a blanking operation to punch out a circular plate; subjecting the circular plate to a drawing operation to produce a cylindrical-container consisting of a cylindrical wall and a bottom wall at one of opposite axial ends of the cylindrical wall: and subjecting the bottom wall to a blanking operation to form an opening through the bottom wall, for thereby forming the inward flange, such that the opening has a profile similar to an inner profile of the annular member. This arrangement permits the ring members to be formed from the blank in the form of a strip with a high yield ratio.
In a third preferred form of this invention, the process further comprises a step of preparing the cylindrical member which includes a cylindrical wall and an outward flange as the above-indicated flange at one of opposite axial ends of the cylindrical wall, the inward flange being formed by plastic deformation when the cylindrical member is formed such that the outward flange extends radially outwardly of the cylindrical wall, and wherein the outward flange as formed by plastic deformation is further subjected to plastic deformation in the above-indicated step of applying a force to the cylindrical member and the above-indicated step of effecting a shearing operation. This preferred form of the invention has substantially the same advantage as the second preferred form of the invention described above.
The annular member may be a ring member having circular inner and outer profile, or any other member having elliptical or other inner and outer profiles.